1. Field of the Invention
The present invention relates to a transceiver to be used for data communications between wearable computers (computers to be worn) for example, and more particularly to a transceiver for inducing electric fields based on data to be transmitted in an electric field propagating medium and carrying out transmission and reception of data by using the induced electric fields.
The present invention also relates to an electric field detecting optical device for detecting electric fields based on transmission data which are induced in and propagated through an electric field propagating medium such as a living body and converting them into electric signals in such a transceiver.
The present invention also relates to a photodetection circuit for detecting lights with optical characteristics changed by the detected electric fields and converting them into electric signals in such an electric field detecting optical device.
2. Description of the Related Art
Due to the progress in reducing size and improving performance of portable terminals, the wearable computers are attracting attentions. FIG. 1 shows an exemplary case of using such wearable computers by wearing them on a human body. As shown in FIG. 1, the wearable computers 1 are put on arms, shoulders, torso, etc., of the human body through respective transceivers 3 and capable of carrying out mutual data transmission and reception as well as communications with an externally provided PC 5 via a cable through transceivers 3a and 3b attached at tip ends of a hand and a leg.
The transceiver 3 to be used for data communications between the wearable computers 1 in such a way is utilizing the signal detection technique based on the electro-optic method using laser lights and electro-optic crystals, in which electric fields based on data to be transmitted are induced in a living body which is an electric field propagating medium and data transmission and reception are carried out by using the induced electric fields.
FIG. 2 shows an exemplary configuration of the transceiver 3, which has an I/O (Input/Output) circuit 101 through which the transceiver 3 is connected to the wearable computer 1, and a transmission electrode 105 and a reception electrode 107 provided in a vicinity of the living body 100 through insulation films 106 and 108 respectively. In this transceiver 3, the electric fields based on the transmission data are induced in the living body 100 from the transmission electrode 105 through the insulation film 106, and the electric fields induced at the other portion of the living body 100 and propagated through the living body 100 are received at the reception electrode 107 through the insulation film 108.
More specifically, in this transceiver 3, when the transmission data from the wearable computer 1 are received through the I/O circuit 101, these transmission data are supplied to a transmission circuit 103 after adjusting their level at a level adjustment circuit 102. The transmission circuit 103 supplies the level adjusted transmission data to the transmission electrode 105, and the electric fields based on the transmission data are induced in the living body 100 from the transmission electrode 105 through the insulation film 100, such that the induced electric fields are propagated to the transceiver 3 provided at the other portion of the living body 100.
On the other hand, when the electric fields induced at the other portion of the living body 100 and propagated through the living body 100 are received at the reception electrode 107 provided in a vicinity of the living body 100 through the insulation film 108, the received electric fields are coupled to an electric field detecting optical unit 110, converted into electric signals by the electro-optic method using laser light and electro-optic element at the electric field detecting optical unit 110, and supplied to a signal processing circuit 109.
In further detail, as shown in FIG. 3, the electric fields are coupled to an electro-optic crystal 131 onto which the laser light from a laser light source 133 is injected, so as to change the polarization state of the laser light. The changes of the polarization state of the laser light are then detected and converted into electric signals by a polarization detecting optical system 135, and supplied to the signal processing circuit 109. Here, the laser light source 133 is operated by currents supplied from a current source 137.
The signal processing circuit 109 applies signal processings such as low noise amplification, noise removal, waveform shaping, etc., with respect to the electric signals from the electric field detecting optical unit 110 or the polarization detecting optical system 135, and supplies them to the wearable computer 1 through the I/O circuit 101.
In the above described conventional transceiver, the transmission circuit 103 and the level adjustment circuit 102 are always connected to the transmission electrode 105, so that while the reception electrode 107 are in a process of receiving the electric fields based on the transmission data from the other portion of the living body 100, the noises from a power source or the like are supplied to the transmission electrode 105 from the transmission circuit 103 and the level adjustment circuit 102, and the electric fields due to these noises are induced in the living body 100 from the transmission electrode 105 and propagated not only to the same transceiver 3 but also to the reception electrode 107 of the other transceiver 3 as well, and this can be a cause of the operation error.
Also, in the above described conventional transceiver, after the level adjustment of the transmission data received from the wearable computer 1, the electric fields are induced in the living body 100 from the transmission circuit 103 through the transmission electrode 105 and the insulation film 106 and propagated through the living body 100, and these electric fields are received through the insulation film 108 and the reception electrode 107 at the other portion of the living body 100. However, the electric fields induced in and propagated through the living body 100 in this manner have weak levels, so that they have a poor S/N ratio, a high probability for causing the operation error, and a poor reliability.
Also, the above described transceiver requires the power consumption to be as small as possible because it is to be used by being put on the living body 100 along with the wearable computer 1. On the other hand, there is no need for the laser light source 133 to be operated all the times. For example, there is no need to operate the laser light source 133 at a time of transmission at which the electric fields are not to be received. However, in the above described conventional transceiver, the laser light source 133 is always operated to generate the laser light so that it is always possible to detect the electric fields induced in and propagated through the living body 100. Consequently, there has been wasteful power consumption as the laser light source 133 is operated even in a state where there is no need to operate the laser light source 133 such as the transmission state in particular.
Also, for the sake of the practical realization of such a wearable computer, the scheme for data communications between the wearable computers is very important, and the conventionally available scheme for data communications between the wearable computers include a scheme for carrying out wired communications by connecting the transceivers connected to the wearable computers by a data line and a ground line, a scheme for carrying out radio communications by connecting the transceivers by radio, and a scheme for carrying out data transmission and reception by using the living body as a signal line and the Earth ground with which the living body is in contact as a ground line (see PAN: Personal Area Network, IBM SYSTEMS JOURNAL, Vol. 35, Nos. 3 & 4, pp. 609-617, 1996).
However, the wired communication scheme requires to connect the transceivers by two cable lines, and in the case of carrying out data transmission and reception between distant wearable computers or among a plurality of wearable computers, it becomes necessary to arrange many cable lines all over the body so that it is not practical.
Also, the radio communication scheme has a possibility of crosstalking with the other systems existing nearby depending on the radio frequencies and powers.
Also, the wearable computers are expected to be mostly put on the upper half body in general, but the communication scheme utilizing the living body as a signal path has a practical problem in this regard in that the communications become impossible when the transceiver of the wearable computer is arranged far from the Earth ground such as at the head for example.
FIG. 4 shows another exemplary configuration of the transceiver 3, which has the I/O circuit 101 through which the transceiver 3 is connected to the wearable computer 1, and the transmission electrode 105 and the reception electrode 107 provided in a vicinity of the living body 100 through the insulation films 106 and 108 respectively, similarly as in the transceiver of FIGS. 2 and 3.
More specifically, in this transceiver 3, when the transmission data from the wearable computer 1 are received through the I/O circuit 101, these transmission data are supplied to a transmission circuit 103 after adjusting their level at a level adjustment circuit 102. The transmission circuit 103 supplies the level adjusted transmission data to the transmission electrode 105, and the electric fields based on the transmission data are induced in the living body 100 from the transmission electrode 105 through the insulation film 100, such that the induced electric fields are propagated to the transceiver 3 provided at the other portion of the living body 100.
On the other hand, when the electric fields induced at the other portion of the living body 100 and propagated through the living body 100 are received at the reception electrode 107 provided in a vicinity of the living body 100 through the insulation film 108, the received electric fields are coupled to an electric field detecting optical unit 110, converted into intensity changes of lights composed of P-polarization components and S-polarization components by the electro-optic method using laser light and electro-optic element at the electric field detecting optical unit 110, and supplied to a photodetection circuit 120.
The photodetection circuit 120 converts the light signals composed of P-polarization components and the S-polarization components from the electric field detecting optical unit 110 into electric signals. These electric signals are then subjected to a noise removal by a band-pass filter 132 and a waveform shaping by a waveform shaping circuit 134, and supplied as received data to the wearable computer 1 through the I/O circuit 101.
The photodetection circuit 120 is formed by a circuit called a balanced detection and single amplification type circuit as shown in FIG. 5, in which a midpoint of first and second photodiodes 91 and 93 that are connected in series between bias voltage sources (+V, −V) is grounded through a load resistor 95 as well as connected to an input of an amplifier 97.
The first and second photodiodes 91 and 93 constituting this conventional photodetection circuit 120 are playing the role of a differential amplifier, and when the light signals with intensity changes in opposite phases composed of P-polarization components and the S-polarization components from the electric field detecting optical unit 110 are detected, the first and second photodiodes 91 and 93 produce currents generated in response to respective light signals such that they are added together at the load resistor 95 to double the currents, and a voltage corresponding to these doubled currents is generated at both ends of the load resistor 95 and supplied as an input voltage to the amplifier 97.
Now, the laser lights generated at the electric field detecting optical unit 110 utilizing the electro-optic method contain noises generated from the laser diode itself or the power source in general. The light signals injected into the first and second photodiodes 91 and 93 of the photodetection circuit 120 from the electric field detecting optical unit 110 that uses such noise mixed laser lights will also contain noises, so that there is a need to remove these noises. In the photodetection circuit of FIG. 5, such noises mixed in the laser lights have the same phase and same level so that they are removed by the balanced detection made by the first and second photodiodes 91 and 93 and the load resistor 95, and they will not be entered into the amplifier 97.
However, the noises mixed at the photodetection circuit as shown in FIG. 5 include not only the noises mixed in the laser lights but also noises mixed into output current signals of the photodiodes via a metallic casing that covers outer sides of the photodiodes 91 and 93, for example. Such noises do not necessarily have the same phase and same level unlike the noises mixed in the laser lights, and the noise levels may vary depending on the positional relationship between the noise source and the photodiodes 91 and 93 or on the way in which the noises are mixed, so that they cannot be removed by the conventional photodetection circuit such as that shown in FIG. 5.